Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations

Which compound in each of the following pairs will react faster in an S_N2 reaction with OH^- ?

(d) ${\mathrm{CH}}_2=\mathrm{CHBr} \mathrm{or} {\mathrm{CH}}_2={\mathrm{CHCH}}_2\mathrm{Br}$

Which reactant in each of the following pairs is more nucleophilic? Explain.  

a) NH₂^- or NH₃

Which reactant in each of the following pairs is more nucleophilic? Explain.  

b) H₂O or CH₃CO₂^-

Which reactant in each of the following pairs is more nucleophilic? Explain.  

a) BF₃ or F^-

Which reactant in each of the following pairs is more nucleophilic? Explain.  

d) (CH₃)₃P or (CH₃)₃N

Which reactant in each of the following pairs is more nucleophilic? Explain.  

(e) I^-  or Cl^-

Which reactant in each of the following pairs is more nucleophilic? Explain.  

F) $\mathrm{C}\equiv {\mathrm{N}}^{- }\mathrm{or} {}^{-}{\mathrm{OCH}}_3$

Compound X is optically inactive and has the formula ${\mathrm{C}}_{16}{\mathrm{H}}_{16}{\mathrm{Br}}_2$. On treatment with strong base, X gives hydrocarbon Y, ${\mathrm{C}}_{16}{\mathrm{H}}_{14}$. Compound Y absorbs 2 equivalents of hydrogen when reduced over a palladium catalyst and reacts with ozone to give two fragments. One fragment, Z, is an aldehyde with formula ${\mathrm{C}}_7{\mathrm{H}}_6\mathrm{O}$. The other fragment is glyoxal, ${\left(\mathrm{CHO}\right)}_2$. Write the reactions involved, and suggest structures for X, Y, and Z. What is the stereochemistry of X? 

When primary alcohol is treated with p-toluenesulfonyl chloride at room temperature in the presence of an organic base such as pyridine, a tosylate is formed. When the same reaction is carried out at a higher temperature, an alkyl chloride is often formed. Explain.

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(a)  NaNH₂

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(b) KOC(CH₃)

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(c)  NaI

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(d) NaCN

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(e) ${\text{Na}}^{+ {-}^{}}\text{C≡CH}$

Question: What products would you expect from the reaction of 1-bromopropane with each of the following? 

(f) Mg, then H₂O

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?

Predict the product(s) for each elimination reaction below. In each case show the mechanism. What do the mechanisms have in common? Why?

a.

b.

c.

Predict the product of each reaction below and indicate if the mechanism is likely to be ${\mathbf{SN}}_1\mathbf{,}{\mathbf{SN}}_2\mathbf{,}{\mathbf{E}}_1\mathbf{,}{\mathbf{E}}_2{\mathbf{orE}}_{1\mathrm{cB}}$

Propose a mechanism for the following reaction, an important step in the laboratory synthesis of proteins:

Draw all isomers of $C_4{H}_{9}Br$, name them, and arrange them in order of decreasing reactivity in the  $S_{N}2$reaction:

The following Walden cycle has been carried out. Explain the results, and indicate where Walden inversion occurs.

Which compound in each of the following pairs will react faster in an $S_{N}2$reaction with $O{H}^{-}$?

$C{H}_{3}BrorC{H}_{3}I$

What effect would you expect the following changes to have on the reaction rate of 1-iodo-2-methylbutane with cyanide ion? 

(a) The  $C{N}^{-}$concentration is halved, and the 1-iodo-2-methylbutane concentration is doubled. 

(b) Both the  $C{N}^{-}$and the 1-iodo-2-methylbutane concentrations are tripled.

What effect would you expect the following changes to have on the rate of the reaction of 1-iodo-2-methylbutane with cyanide ion? 

(b) Both the  and the 1-iodo-2-methylbutane concentrations are tripled.

What effect would you expect the following changes to have on the rate of the reaction of ethanol with 2-iodo-2-methyl butane?

 (a) The concentration of the halide is tripled.

What effect would you expect the following changes to have on the rate of the reaction of ethanol with 2-iodo-2-methyl butane?

(b) The concentration of the ethanol is halved by adding diethyl ether as an inert solvent.

How might you prepare each of the following molecules using a nucleophilic substitution reaction at some step?

(a)

How might you prepare each of the following molecules using a nucleophilic substitution reaction at some step?

How might you prepare each of the following molecules using a nucleophilic substitution reaction at some step?

$c.C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}CN$

How might you prepare each of the following molecules using a nucleophilic substitution reaction at some step?

$d.C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}N{H}_2$

Which reaction in each of the following pairs would you expect to be faster? 

(a) The  $S_{N}2$displacement by $I^{-}onC{H}_{3}ClorC{H}_{3}OTs$

Which reaction in each of the following pairs would you expect to be faster? 

(b) The  displacement by  on bromoethane or on bromocyclohexane

Which reaction in each of the following pairs would you expect to be faster? 

(c) The  $S_{N}2$ displacement on 2-bromopropane by  $C{H}_{3}C{H}_2{O}^{-}$ or by $C{N}^{-}$

Which reaction in each of the following pairs would you expect to be faster? 

(d) The  displacement by on bromomethane in benzene or in acetonitrile

Question: Predict the product and give the stereochemistry resulting from reaction of each of the following nucleophiles with (R)-2-bromooctane: 

a)  $C{N}^{-}$

Question: Predict the product and give the stereochemistry resulting from reaction of each of the following nucleophiles with (R)-2-bromooctane: 

(b) $C{H}_{3}C{O_2}^{-}$

Question: Predict the product and give the stereochemistry resulting from reaction of each of the following nucleophiles with (R)-2-bromooctane: 

(c) $C{H}_3{S}^{-}$

Question: (R)-2-Bromooctane undergoes racemization to give ($\pm$)-2-bromooctane when treated with NaBr in dimethyl sulfoxide. Explain.

Question:  Propose structures for compounds that fit the following descriptions:

(a) An alkyl halide that gives a mixture of three alkenes on E₂ reaction

Question:  Propose structures for compounds that fit the following descriptions:

(b) An organohalide that will not undergo nucleophilic substitution

Question:  Propose structures for compounds that fit the following descriptions:

(c) An alkyl halide that gives the non-Zaitsev product on reaction

Question:  Propose structures for compounds that fit the following descriptions: 

(d) An alcohol that reacts rapidly with HCl at 0 °C

Question: 1-Chloro-1,2-diphenylethane can undergo E2 elimination to give either cis- or trans-1,2-diphenylethylene (stilbene). Draw Newman projections of the reactive conformations leading to both possible products, and suggest a reason why the trans alkene is the major product.

Question: Predict the major alkene product of the following E1 reaction:

Question: There are eight diastereomers of 1,2,3,4,5,6-hexachlorocyclohexane. Draw each in its more stable chair conformation. One isomer loses HCl in an E2 reaction nearly 1000 times more slowly than the others. Which isomer reacts so slowly, and why?

Question: The reactions shown below are unlikely to occur as written. Tell what is wrong with each, and predict the actual product.

b.

Question: The reactions shown below are unlikely to occur as written. Tell what is wrong with each, and predict the actual product.

c.

Question: The reactions shown below are unlikely to occur as written. Tell what is wrong with each, and predict the actual product.

a.

Question: Arrange the carbocations below in order of increasing stability.

a.